LeetCode - Reverse Linked List

 1 // 1CE, 1AC, not perfect
 2 /**
 3  * Definition for singly-linked list.
 4  * struct ListNode {
 5  *     int val;
 6  *     ListNode *next;
 7  *     ListNode(int x) : val(x), next(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     ListNode* reverseList(ListNode* head) {
13         if (head == NULL) {
14             return NULL;
15         }
16         
17         ListNode *p1 = head;
18         ListNode *p2 = p1->next;
19         p1->next = NULL;
20         ListNode *p3;
21         while (p2 != NULL) {
22             p3 = p2->next;
23             p2->next = p1;
24             p1 = p2;
25             p2 = p3;
26         }
27         return p1;
28     }
29 };